It's somewhat implied by the dialogue and some plot elements that the characters in the original version of the story might have been humans rather than Steambots.
A lot of dialogue in this game is strange coming from robots from the Steamworld series. In the very beginning of the game, Armilly wants to eat the mushroom Copernica is looking for because she's hungry. Galleo takes some buns early in the plot and eats them as well. A need or desire to eat is not present among Steambots generally, who run off of burner fuel and water.
In fact, no mention whatsoever is made at all during the story of Steambots, or any of the usual language used to describe Steambots including references to robots, parts, oil, being 'scrapped' instead of killed, or water/boilers. Considering how prevalent this was for flavor or plot in previous games, it's a red flag.
Further dialogue does suggest that the characters might have supposed to have been humans. In the dark cave that turns out to be where Bob is chopping up people to sacrifice them, Armilly says she feels "something slimy and disgusting", which turns out to be the inside of Galleo's mouth. This is an odd thing to be true of a robot. Similar evidence comes in the mountains, as Tarah comments on feeling like her eyelids are going to freeze. While this is slightly less damning counter-evidence against characters being robots, it's still an odd detail for a robot to include.
Quest does not fit into the continuity established by the other Steamworld games, and doesn't make sense as something that happened as told.
The most significant argument for the characters being Steambots is that the book's art depicts them as such, which can be countered that the book was reprinted or remade by Steambots later, who re-imagined the characters as Steambots.
All Retro-specters have been established to be illusions, so what's the deal with all the Moonjuice becoming real items? I checked my inventory after the cutscene.
Moonjuice is probably distilled spirits. Er, the ghostly kind.
